Systems, devices, and methods for narrow waveband laser diodes

ABSTRACT

Systems, devices, and methods for narrow waveband laser diodes are described. The conventional coating on the output facet of a laser diode is replaced with a notch filter coating that is reflective of wavelengths within a narrow waveband around the nominal output wavelength of the laser diode and transmissive of other wavelengths. The notch filter coating ensures the laser diode will lase at the nominal wavelength and not lase for wavelengths outside of the narrow waveband. The notch-filtered laser diode provides a narrow waveband output that is matched to the playback wavelength of at least one hologram in a transparent combiner of a wearable heads-up display, and thereby reduces or eliminates display aberrations that can result from wavelength sensitivity of the playback properties of the hologram.

TECHNICAL FIELD

The present systems, devices, and methods generally relate to laserdiodes having a narrow output waveband and particularly relate towearable heads-up displays that employ laser diodes having a narrowoutput waveband.

BACKGROUND Description of the Related Art

Wearable Heads-UP Displays

A head-mounted display is an electronic device that is worn on a user'shead and, when so worn, secures at least one electronic display within aviewable field of at least one of the user's eyes, regardless of theposition or orientation of the user's head. A wearable heads-up displayis a head-mounted display that enables the user to see displayed contentbut also does not prevent the user from being able to see their externalenvironment. The “display” component of a wearable heads-up display iseither transparent or at a periphery of the user's field of view so thatit does not completely block the user from being able to see theirexternal environment. Examples of wearable heads-up displays include:the Google Glass®, the Optinvent Ora®, the Epson Moverio®, and the SonyGlasstron®, just to name a few.

The optical performance of a wearable heads-up display is an importantfactor in its design. When it comes to face-worn devices, however, usersalso care a lot about aesthetics. This is clearly highlighted by theimmensity of the eyeglass (including sunglass) frame industry.Independent of their performance limitations, many of the aforementionedexamples of wearable heads-up displays have struggled to find tractionin consumer markets because, at least in part, they lack fashion appeal.Most wearable heads-up displays presented to date employ large displaycomponents and, as a result, most wearable heads-up displays presentedto date are considerably bulkier and less stylish than conventionaleyeglass frames.

A challenge in the design of wearable heads-up displays is to minimizethe bulk of the face-worn apparatus will still providing displayedcontent with sufficient visual quality. There is a need in the art forwearable heads-up displays of more aesthetically-appealing design thatare capable of providing high-quality images to the user withoutlimiting the user's ability to see their external environment.

BRIEF SUMMARY

A laser diode may be summarized as including: a layer of p-typesemiconductor material; a layer of n-type semiconductor material; alayer of optically active material disposed between the layer of p-typesemiconductor material and the layer of n-type semiconductor material; areflective rear facet at a first end of the layer of optically activematerial; a partially reflective output facet at a second end of thelayer of optically active material, the second end opposite the firstend across a length of the layer of optically active material to definea laser cavity at least partially bounded by the layer of p-typesemiconductor material, the layer of n-type semiconductor material, thereflective rear facet, and the partially reflective output facet; and atleast one notch filter coating applied to at least one of the reflectiverear facet and the partially reflective output facet. The at least onenotch filter coating may be at least partially reflective of lightwithin a narrow waveband and substantially transmissive of light outsideof the narrow waveband.

The at least one notch filter coating may have a first reflectivity forlight that is within the narrow waveband and a second reflectivity forlight that is outside of the narrow waveband. The first reflectivity forlight that is within the narrow waveband may be at least twice thesecond reflectivity for light that is outside of the narrow waveband.The first reflectivity for light that is within the narrow waveband maybe greater than 70% and the second reflectivity for light that isoutside of the narrow waveband may be less than 30%.

The narrow waveband may have a bandwidth of less than 10 nm. The narrowwaveband may be centered on a nominal output wavelength of the laserdiode. The narrow waveband may include a gain peak of the laser diode.

The at least one notch filter coating may include a rugate device.

The at least one notch filter coating may be applied to the reflectiverear facet and not to the partially reflective output facet. The atleast one notch filter coating may be applied to the partiallyreflective output facet and not to the reflective rear facet. The atleast one notch filter coating may be applied to both the reflectiverear facet and the partially reflective output facet; that is, the atleast one notch filter may include a first notch filter coating appliedto the partially reflective output facet and a second notch filtercoating applied to the reflective rear facet.

A wearable heads-up display may be summarized as including: a supportstructure that in use is worn on a head of a user of the wearableheads-up display; a transparent combiner carried by the supportstructure and positioned in a field of view of an eye of the user whenthe support structure is worn on the head of the user, wherein thetransparent combiner includes at least one holographic optical element;and a laser projector carried by the support structure and positionedand oriented to project laser light onto the at least one holographicoptical element, wherein the laser projector includes at least one laserdiode and the at least one laser diode comprises: a layer of p-typesemiconductor material; a layer of n-type semiconductor material; alayer of optically active material disposed between the layer of p-typesemiconductor material and the layer of n-type semiconductor material; areflective rear facet at a first end of the layer of optically activematerial; a partially reflective output facet at a second end of thelayer of optically active material, the second end opposite the firstend across a length of the layer of optically active material to definea laser cavity at least partially bounded by the layer of p-typesemiconductor material, the layer of n-type semiconductor material, thereflective rear facet, and the partially reflective output facet; and atleast one notch filter coating applied to at least one of the reflectiverear facet and the partially reflective output facet. The at least onenotch filter coating may be at least partially reflective of lightwithin a narrow waveband and substantially transmissive of light outsideof the narrow waveband.

The at least one notch filter coating may have a first reflectivity forlight that is within the narrow waveband and a second reflectivity forlight that is outside of the narrow waveband. The first reflectivity forlight that is within the narrow waveband may be at least twice thesecond reflectivity for light that is outside of the narrow waveband.The first reflectivity for light that is within the narrow waveband maybe greater than 70% and the second reflectivity for light that isoutside of the narrow waveband may be less than 30%.

The narrow waveband may have a bandwidth of less than 10 nm. The narrowwaveband may be centered on a nominal output wavelength of the laserdiode. The narrow waveband may include a gain peak of the laser diode.The holographic optical element may include at least one hologram thatis responsive to light within the narrow waveband.

The at least one notch filter coating may include a rugate device.

The at least one notch filter coating may be applied to the reflectiverear facet and not to the partially reflective output facet. The atleast one notch filter coating may be applied to the partiallyreflective output facet and not to the reflective rear facet. The atleast one notch filter coating may be applied to both the reflectiverear facet and the partially reflective output facet; that is, the atleast one notch filter may include a first notch filter coating appliedto the partially reflective output facet and a second notch filtercoating applied to the reflective rear facet.

A method of fabricating a narrow waveband laser diode may be summarizedas including: forming a laser cavity; positioning a first facet at afirst end of the laser cavity; coating a second facet with a notchfilter coating; and positioning the second facet, with the notch filtercoating applied thereto, at a second end of the laser cavity, the secondend opposite the first end across a length of the laser cavity.

Positioning a first facet at a first end of the laser cavity may includepositioning a reflective rear facet at the first end of the lasercavity. Coating a second facet with a notch filter coating may includecoating a partially reflective output facet with the notch filtercoating. Positioning the second facet, with the notch filter coatingapplied thereto, at a second end of the laser cavity may includepositioning the partially reflective output facet, with the notch filtercoating applied thereto, at the second end of the laser cavity. In someimplementations, the method may further include coating the reflectiverear facet with the notch filter coating prior to positioning thereflective rear facet at the first end of the laser cavity.

Alternatively, positioning a first facet at a first end of the lasercavity may include positioning a partially reflective output facet atthe first end of the laser cavity. Coating a second facet with a notchfilter coating may include coating a reflective rear facet with thenotch filter coating. Positioning the second facet, with the notchfilter coating applied thereto, at a second end of the laser cavity mayinclude positioning the reflective rear facet, with the notch filtercoating applied thereto, at the second end of the laser cavity.

Forming a laser cavity may include forming a laser cavity comprising alayer of p-type semiconductor material, a layer of n-type semiconductormaterial, and a layer of optically active material disposed between thelayer of p-type semiconductor material and the layer of n-typesemiconductor material.

Coating a second facet with a notch filter coating may include coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband. Coating the secondfacet with a notch filter coating that is at least partially reflectiveof light within a narrow waveband and substantially transmissive oflight outside of the narrow waveband may include coating the secondfacet with a notch filter coating that has a first reflectivity forlight that is within the narrow waveband and a second reflectivity forlight that is outside of the narrow waveband, wherein the firstreflectivity for light that is within the narrow waveband is at leasttwice the second reflectivity for light that is outside of the narrowwaveband. Coating the second facet with a notch filter coating that hasa first reflectivity for light that is within the narrow waveband and asecond reflectivity for light that is outside of the narrow waveband mayinclude coating the second facet with a notch filter coating that has afirst reflectivity greater than 70% for light that is within the narrowwaveband and a second reflectivity less than 30% for light that isoutside of the narrow waveband.

Coating the second facet with a notch filter coating that is at leastpartially reflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband may include coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband of less than 10 nm andsubstantially transmissive of light outside of the narrow waveband ofless than 10 nm.

Coating the second facet with a notch filter coating that is at leastpartially reflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband may include coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband centered on a nominaloutput wavelength of the laser diode and substantially transmissive oflight outside of the narrow waveband centered on the nominal outputwavelength of the laser diode.

Coating the second facet with a notch filter coating that is at leastpartially reflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband may include coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband that includes a gain peakof the laser diode and substantially transmissive of light outside ofthe narrow waveband that includes the gain peak of the laser diode.

Coating a second facet with a notch filter coating may include coatingthe second facet with a rugate device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not necessarily drawn to scale, and some ofthese elements are arbitrarily enlarged and positioned to improvedrawing legibility. Further, the particular shapes of the elements asdrawn are not necessarily intended to convey any information regardingthe actual shape of the particular elements, and have been solelyselected for ease of recognition in the drawings.

FIG. 1 is an illustrative diagram showing a side view of a wearableheads-up display that employs a scanning laser projector.

FIG. 2 is a sectional view of a laser diode having a narrow outputwaveband in accordance with the present systems, devices, and methods.

FIG. 3 is an illustrative diagram showing a side view of a wearableheads-up display that employs a scanning laser projector having at leasta green laser diode with a notch filter coating in accordance with thepresent systems, devices, and methods.

FIG. 4 is a partial-cutaway perspective view of a wearable heads-updisplay that employs laser diodes with notch filter coating appliedthereto (e.g., to the output facets thereof) to provide narrow wavebandlaser light and reduce display aberrations in accordance with thepresent systems, devices, and methods.

FIG. 5 is a flow-diagram showing a method of fabricating a narrowwaveband laser diode in accordance with the present systems, devices,and methods.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with portable electronicdevices and head-worn devices, have not been shown or described indetail to avoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its broadest sense, that is as meaning “and/or”unless the content clearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

The various embodiments described herein provide systems, devices, andmethods for laser diodes with narrow waveband outputs. Such isconventionally achieved in the art by coupling the output of a laserdiode into an external component, such as a volume Bragg grating, thatresides outside of and apart from the laser diode itself. Whileappropriate for some applications, external components such as volumeBragg gratings are expensive and can add considerable volume and bulk toa laser diode, which is particularly disadvantageous in applications forwhich compact laser diodes are desired.

An example of an application for which compact laser diodes are desiredis in a wearable heads-up display (“WHUD”) that employs one or morelaser diode(s) as a light source for generating display images. Forexample, the present systems, devices, and methods are well-suited foruse in WHUDs that employ a scanning laser projector (“SLP”) including atleast one laser diode. Examples of such displays are described in U.S.Provisional Patent Application Ser. No. 62/017,089; U.S. ProvisionalPatent Application Ser. No. 62/053,598; U.S. Provisional PatentApplication Ser. No. 62/117,316; U.S. Provisional Patent ApplicationSer. No. 62/134,347 (now U.S. Non-Provisional patent application Ser.No. 15/070,887); U.S. Provisional Patent Application Ser. No.62/156,736; U.S. Provisional Patent Application Ser. No. 62/242,844; USPatent Publication No. US 2015-0378164 A1; US Patent Publication No. US2015-0378161 A1; US Patent Publication No. US 2015-0378162 A1; U.S.Non-Provisional patent application Ser. No. 15/145,576; U.S.Non-Provisional patent application Ser. No. 15/145,609; U.S.Non-Provisional patent application Ser. No. 15/145,583; U.S.Non-Provisional patent application Ser. No. 15/046,234; U.S.Non-Provisional patent application Ser. No. 15/046,254; and U.S.Non-Provisional patent application Ser. No. 15/046,269. A generalizedexample of such a WHUD architecture is provided in FIG. 1.

FIG. 1 is an illustrative diagram showing a side view of a WHUD 100 thatemploys a SLP 110. SLP 110 comprises a laser module 111 that includes ared laser diode (labelled “R” in FIG. 1), a green laser diode (labelled“G” in FIG. 1), and a blue laser diode (labelled “B” in FIG. 1), and ascan mirror 112 that is controllably rotatable about two axes offreedom. A single scan mirror 112 that is rotatable about two axes offreedom is used only as an illustrative example herein and a person ofskill in the art will appreciate that similar functionality may berealized using a different mirror configuration, such as for example twoscan mirrors that are each controllably rotatable about a respective oneof two orthogonal axes of freedom and respectively positioned insequence with respect to the optical path of laser light 120. Laserlight 120 output by SLP 110 may comprise any modulated combination ofred laser light (output by the red laser diode), green laser light(output by the green laser diode), and/or blue laser light (output bythe blue laser diode). For ease of illustration, laser light 120 in FIG.1 is shown comprising only green laser light.

Laser light 120 reflected from scan mirror 112 is, in the illustratedexemplary implementation of a WHUD shown in FIG. 1, incident on aholographic optical element (“HOE”) 130 that redirects laser light 120back towards an eye 190 of a user. Generally, in the present systems,devices, and methods, the term “user” refers to a user of a laser diode.In the specific context of FIG. 1, the term “user” refers to a personwearing or using WHUD 100. A person of skill in the art will appreciatethat WHUD 100 may include a support frame and/or other support/alignmentstructure(s) (not depicted in FIG. 1 to reduce clutter) that enable auser to wear the elements depicted in FIG. 1 so that at least HOE 130 ispositioned within a field of view of at least one eye 190 of the userwhen WHUD 100 is worn on a head of the user. A person of skill in theart will also appreciate that alternative WHUD architectures that employlaser diodes and HOEs may similarly be employed, such as for example anarchitecture in which HOE 130 is carried by an optical waveguide orlightguide and, for example, serves as a holographic in-coupler orout-coupler therefor.

HOE 130 may be substantially optically transparent to environmentallight 140 (i.e., optically transparent to the majority of wavelengthsthat make up environmental light 140) incident from the opposite side ofHOE 130 relative to laser light 120. Because HOE 130 effectivelycombines projected laser light 120 and external environmental light 140in the user's field of view, HOE 130 may be referred to as a “combiner”or related variant, such as “transparent combiner,” “holographic opticalcombiner,” or similar (or as a component of such a combiner). If thesupport frame (not illustrated) of WHUD 100 has the general shape,appearance, and/or geometry of a pair of eyeglasses, then HOE 130 may becarried on one or more transparent lens(es) of WHUD 100 (such as one ormore prescription lenses or one or more non-prescription lenses).Further details on the composition of HOE 130 (e.g., including exemplarymultiplexed configurations of HOE 130) and on ways in which HOE 130 mayredirect laser light 120 towards eye 190 (e.g., including exemplary exitpupil and eyebox configurations) are described in at least the patentapplications listed above.

The playback properties of a holographic optical element (e.g., ahologram) can be particularly sensitive to a number of factors,including properties of the light that is incident thereon. For example,the playback properties of HOE 130 are particularly sensitive to theangle and wavelength of incident laser light 120. In FIG. 1, incidentlaser light 120 is shown having a single angle of incidence on HOE 130but reflecting over a small range 121 of angles of reflection. This isbecause even though laser light 120 only comprises “green” laser lightin the illustrated example of FIG. 1, the green laser diode (labelled Gin FIG. 1) that outputs green laser light 120 does so over a certainwaveband comprising multiple green wavelengths. The sensitivity of HOE130 to incident wavelength is such that the bandwidth of green laserlight 120 output by the green laser diode in projector 110 produces arange 121 of reflection angles at HOE 130, even for a fixed incidenceangle. This small range 121 of reflection angles is undesirable in WHUD100 because it adversely affects display quality. For example, in theillustration of FIG. 1, a single green dot is being displayed to theuser and even though SLP 110 is projecting the green dot to a singlelocation in the user's field of view the dot may appear to “wobble” overrange 121 of reflection angles in correspondence with the bandwidth ofgreen laser light output by the green laser diode. The present systems,devices, and methods provide laser diodes having narrow output wavebandsthat are particularly well-suited to reducing the range 121 ofreflection angles corresponding to each incidence point on HOE 130 andthereby reducing (ideally eliminating) this “wobble” effect.

FIG. 2 is a sectional view of a laser diode 200 having a narrow outputwaveband in accordance with the present systems, devices, and methods.Laser diode 200 comprises: a layer of p-type semiconductor material 201,a layer of n-type semiconductor material 202, a layer of opticallyactive material 210 disposed between layer of p-type semiconductormaterial 201 and layer of n-type semiconductor material 202, areflective rear facet 221 at a first end 211 of layer of opticallyactive material 210; a partially reflective output facet 222 at a secondend 212 of layer of optically active material 210, second end 212opposite first end 211 across a length of layer of optically activematerial 210 to define a laser cavity 250 at least partially bounded bylayer of p-type semiconductor material 201, layer of n-typesemiconductor material 202, reflective rear facet 221, and partiallyreflective output facet 222, and at least one notch filter coating 260applied to at least one of reflective rear facet 221 and partiallyreflective output facet 222. In the illustrated example of FIG. 2, onlya single notch filter coating 260 is applied to partially reflectiveoutput facet 222 and no notch filter coating is applied to reflectiverear facet 221; however, in alternative implementations multiple notchfilter coating 260 may be applied to partially reflective output facet222, and/or at least one additional notch filter coating may be appliedto reflective rear facet 221 such that both partially reflective outputfacet 222 and reflective rear facet 221 have at least one respectivenotch filter coating 260 applied thereto, and/or notch filter coating260 may not be applied to partially reflective output facet 222 at alland instead at least one notch filter coating may be applied only toreflective rear facet 221.

Notch filter coating 260 may, for example, employ common coating oxidessuch as SiO2, TiO2, Al2O3, And/or Ta2O5, and/or common coating fluoridessuch as MgF2, LaF3, and/or AlF3. Notch filter coating 260 may, forexample, employ similar materials to Bragg reflector coatings, exceptthat the design wavelength may be shifted such that out-of-bandoscillations overlap the lasing region of the laser spectrum. Forexample, notch filter coating 260 may employ alternating layers ofdielectric and metallic materials, such as tantalum pentoxide and/oraluminum oxide. There are many material compositions that may achieve adesired notch filter coating. In general, notch filter coating 260 is atleast partially reflective of light within a narrow waveband andsubstantially transmissive (i.e., about 80% transmissive) of lightoutside of the narrow waveband. Generally, notch filter coating 260 hasa first reflectivity for light that is within the narrow waveband and asecond reflectivity for light that is outside of the narrow waveband. Insome implementations, the first reflectivity for light that is withinthe narrow waveband may be at least twice the second reflectivity forlight that is outside of the narrow waveband. As an example, the firstreflectivity for light that is within the narrow waveband may be greaterthan about 70% and the second reflectivity for light that is outside ofthe narrow waveband may be less than about 30%.

Laser diode 200 includes an optical notch filter 260 integrated with theoutput facet 222 and thereby achieves a narrow waveband output withoutthe need for outcoupling into an expensive and bulky external cavity,such as a volume Bragg grating. Notch filter 260 comprises a coatingapplied directly to output facet 222, where the coating is designed tobe reflective of light in a certain narrow waveband (i.e., the desiredoutput waveband of laser diode 200) and transmissive of light outside ofthat narrow waveband. Notch filter coating 260 may be applied to eitheror both surfaces of output facet 222 and may comprise a gratingstructure, such as for example a rugate device. Since coatings aretypically applied to laser facets anyway, the application of notchfilter coating 260 need not add considerable cost to laser diode 200relative to other laser diodes, and notch filter coating 260 isgenerally less expensive than an external cavity with volume Bragggrating. In some implementations, notch filter 260 may include a filmwhere “coating” output facet 222 with notch filter 260 includes adheringor otherwise affixing notch filter 260 to a surface of output facet 222.

In general, a laser diode may “lase” based on gain and loss as afunction wavelength. The laser may lase wherever (in wavelength) thegain exceeds the loss. Notch filter coating 260 may be transmissive(i.e., lossy) for all wavelengths except those within one narrowwaveband; thus notch filter coating 260 may “keep in” light that is inthe narrow waveband and force laser diode 200 to lase within the narrowwaveband. This may be true even if facet 221 is still highly reflectiveover a broadband, and even if notch filter coating 260 has a partialreflectivity of about 80%.

While the gain-bandwidth of the lasing medium (210) can be broad, oncelasing starts at a given wavelength, the available gain typically goes(mostly) into that lasing mode. However, gain competition can resultwhen the selectivity between adjacent modes is so small that smallperturbations can cause mode hops. Notch filter coating 260 may preventmode hops by having higher loss outside the narrow waveband and therebypreventing lasing for wavelengths outside of the narrow waveband.Generally, the physics is substantially similar to that of otherexternal cavity designs in common usage, such as volume Bragg gratings.

As described previously, in some implementations, notch filter coating260 may be applied to rear facet 221 instead of output facet 222, thoughin general it may be more straightforward to fabricate a partiallyreflective notch filter (i.e., an output facet 222 with a notch filtercoating 260) than a fully reflective notch filter (i.e., a rear facet221 with a notch filter coating such as notch filter coating 260).

As described previously, in some implementations, a respective notchfilter coating such as coating 260 (e.g., a first notch filter coatingand a second notch filter coating, respectively) may be applied to bothoutput facet 222 and rear facet 221, but in such implementations thenotch characteristics of both facets may need to be matched which canadd unwanted complexity and cost to the laser diode construction.

The narrow waveband output by laser diode 200 may not be as narrow ascan be achieved by an external cavity with volume Bragg grating, butstill may generally be less than about 10 nm and at considerably lesscost with considerably less volume added to the laser diode. The narrowwaveband of notch filter coating 260 may be centered on a nominal outputwavelength of laser diode 200 and may include a gain peak of laser diode200.

As previously described, notch filter coating 260 may include a customcoating applied to output facet 222 and may, in some implementations,include a rugate device to achieve the desired notch filteringproperties.

FIG. 3 is an illustrative diagram showing a side view of a WHUD 300 thatemploys a SLP 310 having at least a green laser diode (labeled “G” inFIG. 3) with a notch filter coating 360 in accordance with the presentsystems, devices, and methods. WHUD 300 is substantially similar to WHUD100 with the exception that the green laser diode of WHUD 100 had nonotch filter coating whereas the green laser diode of WHUD 300 issubstantially similar to laser diode 200 of FIG. 2 and does have atleast one notch filter coating 360 applied.

In FIG. 3, SLP 310 is projecting green laser light 320 to the same fixedlocation on HOE 330 as SLP 110 was projecting green laser light 120 ontoHOE 130 in FIG. 1; however, because the green laser diode in FIG. 3 hasnotch filter coating 360 applied at the output facet thereof (see FIG.2), green laser light 320 of FIG. 3 is of a much narrower waveband(e.g., bandwidth of less than about 10 nm, or less than about 5 nm, orless than about 3 nm) compared to green laser light 120 of FIG. 1 and,as a result, reflected light 321 is reflected to a point on eye 390rather than over a range 121 of reflection angles as was the case inFIG. 1. In other words, notch filter coating 360 narrows the waveband ofgreen laser light 320 relative to green laser light 120 and therebyreduces (or ideally eliminates as drawn in FIG. 3) the “wobble” effectcaused by the playback sensitivity of HOE 130/330 to the wavelength oflight incident thereon. In this case, the “green dot” displayed to eye390 of the user of WHUD 300 will not appear to wobble as does the “greendot” displayed to eye 190 of the user of WHUD 100, or at least, willappear to wobble to a lesser extent. Such improves the overall displayquality of WHUD 300 relative to that of WHUD 100.

FIG. 4 is a partial-cutaway perspective view of a WHUD 400 that employslaser diodes with notch filter coating applied thereto (e.g., to theoutput facets thereof) to provide narrow waveband laser light and reducedisplay aberrations in accordance with the present systems, devices, andmethods. WHUD 400 includes a support structure 410 that in use is wornon the head of a user and has a general shape and appearance of aneyeglasses (e.g., sunglasses) frame. Support structure 410 carriesmultiple components, including: a SLP 420, a transparent (holographic)combiner 430, and an eyebox expansion optic 450. Portions of SLP 420 andeyebox expansion optic 450 may be contained within an inner volume ofsupport structure 410; however, FIG. 4 provides a partial-cutaway viewin which regions of support structure 410 have been removed in order torender visible portions of SLP 420 and eyebox expansion optic 450 thatmay otherwise be concealed.

Throughout this specification and the appended claims, the term“carries” and variants such as “carried by” are generally used to referto a physical coupling between two objects. The physical coupling may bedirect physical coupling (i.e., with direct physical contact between thetwo objects) or indirect physical coupling that may be mediated by oneor more additional objects. Thus, the term carries and variants such as“carried by” are meant to generally encompass all manner of direct andindirect physical coupling, including without limitation: carried on,carried within, physically coupled to, and/or supported by, with orwithout any number of intermediary physical objects therebetween.

SLP 420 may include multiple laser diodes (e.g., a red laser diode, agreen laser diode, and/or a blue laser diode) and at least one scanmirror (e.g., a single two-dimensional scan mirror or twoone-dimensional scan mirrors, which may be, e.g., MEMS-based orpiezo-based). SLP 420 may be communicatively coupled to (and supportstructure 410 may further carry) a processor and a non-transitoryprocessor-readable storage medium or memory storing processor-executabledata and/or instructions that, when executed by the processor, cause theprocessor to control the operation of SLP 420. For ease of illustration,FIG. 4 does not call out a processor or a memory.

Transparent (holographic) combiner 430 is positioned within a field ofview of at least one eye of the user when support structure 410 is wornon the head of the user. Holographic combiner 430 is sufficientlyoptically transparent to permit light from the user's environment (i.e.,“environmental light”) to pass through to the user's eye. In theillustrated example of FIG. 4, support structure 410 further carries atransparent eyeglass lens 440 (e.g., a prescription eyeglass lens or anon-prescription lens) and holographic combiner 430 comprises at leastone layer of holographic material that is adhered to, affixed to,laminated with, carried in or upon, or otherwise integrated witheyeglass lens 440. The at least one layer of holographic material mayinclude a photopolymer film such as Bayfol® HX available from BayerMaterialScience AG or a silver halide compound and may, for example, beintegrated with transparent lens 440 using any of the techniquesdescribed in U.S. Provisional Patent Application Ser. No. 62/214,600.Holographic combiner 430 includes at least one hologram in or on the atleast one layer of holographic material. With holographic combiner 430positioned in a field of view of an eye of the user when supportstructure 410 is worn on the head of the user, the at least one hologramof holographic combiner 430 is positioned and oriented to redirect lightoriginating from SLP 420 towards the eye of the user. In particular, theat least one hologram is positioned and oriented to receive lightsignals that originate from SLP 420 and converge those light signals toat least one exit pupil at or proximate the eye of the user. Asdescribed previously, in some implementations holographic combiner 430may include an optical waveguide or lightguide through which laser lightfrom SLP 420 is propagated, and the at least one hologram of holographiccombiner 430 may be carried by such optical waveguide or lightguide andprovide the functionality of a holographic in-coupler or out-coupler.

One or more of the laser diode(s) in SLP 420 is/are substantiallysimilar to laser diode 200 from FIG. 2 and include(s) a notch filtercoating applied to the output facet thereof for the purpose of narrowingthe waveband of laser light emitted thereby. This notch filter coatingis relatively inexpensive and takes up virtually no extra space in SLP420 (since the laser diodes will typically have some form of coatingapplied to their output facets anyway), but has considerable benefit inreducing display aberrations by ensuring more consistent and reliableplayback of laser light from holographic combiner 430. This benefit isachieved by matching the narrow waveband output of the one or more laserdiode(s) to the playback wavelength(s) of the one or more hologram(s) inholographic combiner 430. In other words, holographic combiner 430includes at least one hologram that is responsive to light within thenarrow waveband of at least one laser diode, such narrow wavebandprovided by a notch filter coating applied to the output facet of the atleast one laser diode.

FIG. 5 is a flow-diagram showing a method 500 of fabricating a narrowwaveband laser diode in accordance with the present systems, devices,and methods. The narrow waveband laser diode may be substantiallysimilar to laser diode 200 from FIG. 2 and generally includes a notchfilter coating applied to a partially reflective output facet. Method500 includes four acts 501, 502, 503, and 504, though those of skill inthe art will appreciate that in alternative embodiments certain acts maybe omitted and/or additional acts may be added. Those of skill in theart will also appreciate that the illustrated order of the acts is shownfor exemplary purposes only and may change in alternative embodiments.

At 501, a laser cavity is formed. The laser cavity may be substantiallysimilar to laser cavity 250 from FIG. 2 and forming the laser cavity mayinclude forming a laser cavity comprising a layer of p-typesemiconductor material, a layer of n-type semiconductor material, and alayer of optically active material disposed between the layer of p-typesemiconductor material and the layer of n-type semiconductor material.For example, forming the laser cavity may include forming a layer ofn-type semiconductor material (e.g., on a substrate), forming a layer ofoptically active material on the layer of n-type semiconductor material,and forming a layer of p-type semiconductor material on top of the layerof optically active material to dispose the layer of optically activematerial in between the layer of n-type semiconductor material and thelayer of p-type semiconductor material. In alternative implementations,forming the laser cavity may include forming a layer of p-typesemiconductor material (e.g., on a substrate), forming a layer ofoptically active material on the layer of p-type semiconductor material,and forming a layer of n-type semiconductor material on top of the layerof optically active material to dispose the layer of optically activematerial in between the layer of n-type semiconductor material and thelayer of p-type semiconductor material.

At 502, a first facet is positioned at a first end of the laser cavity.The first facet may be a reflective rear facet positioned at a rear orback end of the laser cavity or the first facet may be a partiallyreflective output facet positioned at a front or output end of the lasercavity.

At 503, a second facet is coated with a notch filter coating. Thecoating may, for example, comprise thin layers of dielectric and/ormetallic materials (e.g., oxides, fluorides, etc., as describedpreviously) applied by deposition (e.g., atomic layer deposition,chemical vapor deposition) processes or other known coating processes,such as thermal and electron beam evaporation or sputtering (e.g.,magnetron sputtering, ion beam sputtering, or similar), depending on thethicknesses required.

As described previously, coating a facet with a “notch filter” coatingmay include coating the facet with a coating that is at least partiallyreflective of light within a narrow waveband (e.g., less than about 10nm) that: i) is centered on a nominal output wavelength of the laserdiode; and/or ii) includes a gain peak of the laser diode, andsubstantially transmissive of light outside of such narrow waveband. Thecoating may have a first reflectivity (e.g., about 70% or more) forlight that is within the narrow waveband and a second reflectivity(e.g., about 30% or less) for light that is outside of the narrowwaveband. In some implementations, coating the second facet with a notchfilter coating at 503 may include coating the second facet with a rugatedevice.

At 504, the second facet, with the notch filter coating applied thereto,is positioned at a second end of the laser cavity, the second endopposite the first end across a length of the laser cavity.

In method 500, either one of the “first facet” and the “second facet”may be a reflective rear facet (e.g., 221 in FIG. 2) of the laser diodeand the other one of the “second facet” and the first “facet” may be apartially reflective output facet (e.g., 222 in FIG. 2) of the laserdiode. Similarly, either one of the “first end” and the “second end” ofthe laser cavity may correspond to the rear end of the laser diode andthe other one of the “second end” and the “first end” may correspond tothe output end of the laser diode. That is, in some implementations:positioning a first facet at a first end of the laser cavity at 502includes positioning a reflective rear facet at the first end of thelaser cavity; coating a second facet with a notch filter coating at 503includes coating a partially reflective output facet with the notchfilter coating; and positioning the second facet, with the notch filtercoating applied thereto, at a second end of the laser cavity at 504includes positioning the partially reflective output facet, with thenotch filter coating applied thereto, at the second end of the lasercavity. In such implementations, method 500 may be extended to furtherinclude coating the reflective rear facet with the notch filter coatingprior to positioning the reflective rear facet at the first end of thelaser cavity, such that both the partially reflective output facet andthe reflective rear facet are coated with respective notch filtercoatings prior to being positioned at respective ends of the lasercavity. However, in alternative implementations: positioning a firstfacet at a first end of the laser cavity at 502 includes positioning apartially reflective output facet at the first end of the laser cavity;coating a second facet with a notch filter coating at 503 includescoating a reflective rear facet with the notch filter coating; andpositioning the second facet, with the notch filter coating appliedthereto, at a second end of the laser cavity at 504 includes positioningthe reflective rear facet, with the notch filter coating appliedthereto, at the second end of the laser cavity.

Throughout this specification and the appended claims, the term “about”is sometimes used in relation to specific values or quantities. Forexample, “light within a bandwidth of about 10 nm or less.” Unless thespecific context requires otherwise, the term about generally means±15%.

The WHUDs described herein may include one or more sensor(s) (e.g.,microphone, camera, thermometer, compass, and/or others) for collectingdata from the user's environment. For example, one or more camera(s) maybe used to provide feedback to the processor of the wearable heads-updisplay and influence where on the transparent display(s) any givenimage should be displayed.

The WHUDs described herein may include one or more on-board powersources (e.g., one or more battery(ies)), a wireless transceiver forsending/receiving wireless communications, and/or a tethered connectorport for coupling to a computer and/or charging the one or more on-boardpower source(s).

Throughout this specification and the appended claims the term“communicative” as in “communicative pathway,” “communicative coupling,”and in variants such as “communicatively coupled,” is generally used torefer to any engineered arrangement for transferring and/or exchanginginformation. Exemplary communicative pathways include, but are notlimited to, electrically conductive pathways (e.g., electricallyconductive wires, electrically conductive traces), magnetic pathways(e.g., magnetic media), and/or optical pathways (e.g., optical fiber),and exemplary communicative couplings include, but are not limited to,electrical couplings, magnetic couplings, and/or optical couplings.

Throughout this specification and the appended claims, infinitive verbforms are often used. Examples include, without limitation: “to detect,”“to provide,” “to transmit,” “to communicate,” “to process,” “to route,”and the like. Unless the specific context requires otherwise, suchinfinitive verb forms are used in an open, inclusive sense, that is as“to, at least, detect,” to, at least, provide,” “to, at least,transmit,” and so on.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other portable and/or wearableelectronic devices, not necessarily the exemplary wearable electronicdevices generally described above.

For instance, the foregoing detailed description has set forth variousembodiments of the devices and/or processes via the use of blockdiagrams, schematics, and examples. Insofar as such block diagrams,schematics, and examples contain one or more functions and/oroperations, it will be understood by those skilled in the art that eachfunction and/or operation within such block diagrams, flowcharts, orexamples can be implemented, individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. In one embodiment, the present subject matter may beimplemented via Application Specific Integrated Circuits (ASICs).However, those skilled in the art will recognize that the embodimentsdisclosed herein, in whole or in part, can be equivalently implementedin standard integrated circuits, as one or more computer programsexecuted by one or more computers (e.g., as one or more programs runningon one or more computer systems), as one or more programs executed by onone or more controllers (e.g., microcontrollers) as one or more programsexecuted by one or more processors (e.g., microprocessors, centralprocessing units, graphical processing units), as firmware, or asvirtually any combination thereof, and that designing the circuitryand/or writing the code for the software and or firmware would be wellwithin the skill of one of ordinary skill in the art in light of theteachings of this disclosure.

When logic is implemented as software and stored in memory, logic orinformation can be stored on any processor-readable medium for use by orin connection with any processor-related system or method. In thecontext of this disclosure, a memory is a processor-readable medium thatis an electronic, magnetic, optical, or other physical device or meansthat contains or stores a computer and/or processor program. Logicand/or the information can be embodied in any processor-readable mediumfor use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions associated with logic and/or information.

In the context of this specification, a “non-transitoryprocessor-readable medium” can be any element that can store the programassociated with logic and/or information for use by or in connectionwith the instruction execution system, apparatus, and/or device. Theprocessor-readable medium can be, for example, but is not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus or device. More specific examples (anon-exhaustive list) of the computer readable medium would include thefollowing: a portable computer diskette (magnetic, compact flash card,secure digital, or the like), a random access memory (RAM), a read-onlymemory (ROM), an erasable programmable read-only memory (EPROM, EEPROM,or Flash memory), a portable compact disc read-only memory (CDROM),digital tape, and other non-transitory media.

The various embodiments described above can be combined to providefurther embodiments. To the extent that they are not inconsistent withthe specific teachings and definitions herein, all of the U.S. patents,U.S. patent application publications, U.S. patent applications, foreignpatents, foreign patent applications and non-patent publicationsreferred to in this specification and/or listed in the Application DataSheet which are owned by Thalmic Labs Inc., including but not limitedto: U.S. Provisional Patent Application Ser. No. 62/537,344; U.S.Provisional Patent Application Ser. No. 62/017,089; U.S. ProvisionalPatent Application Ser. No. 62/053,598; U.S. Provisional PatentApplication Ser. No. 62/117,316; U.S. Provisional Patent ApplicationSer. No. 62/134,347 (now U.S. Non-Provisional patent application Ser.No. 15/070,887); U.S. Provisional Patent Application Ser. No.62/156,736; U.S. Provisional Patent Application Ser. No. 62/242,844; USPatent Publication No. US 2015-0378164 A1; US Patent Publication No. US2015-0378161 A1; US Patent Publication No. US 2015-0378162 A1; U.S.Non-Provisional patent application Ser. No. 15/145,576; U.S.Non-Provisional patent application Ser. No. 15/145,609; U.S.Non-Provisional patent application Ser. No. 15/145,583; U.S.Non-Provisional patent application Ser. No. 15/046,234; U.S.Non-Provisional patent application Ser. No. 15/046,254; and U.S.Non-Provisional patent application Ser. No. 15/046,269, are incorporatedherein by reference, in their entirety. Aspects of the embodiments canbe modified, if necessary, to employ systems, circuits and concepts ofthe various patents, applications and publications to provide yetfurther embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A method of fabricating a narrow wavebandlaser diode, the method comprising: forming a laser cavity; positioninga first facet at a first end of the laser cavity; coating a second facetwith a notch filter coating; and positioning the second facet, with thenotch filter coating applied thereto, at a second end of the lasercavity, the second end opposite the first end across a length of thelaser cavity.
 2. The method of claim 1 wherein: positioning a firstfacet at a first end of the laser cavity includes positioning areflective rear facet at the first end of the laser cavity; coating asecond facet with a notch filter coating includes coating a partiallyreflective output facet with the notch filter coating; and positioningthe second facet, with the notch filter coating applied thereto, at asecond end of the laser cavity includes positioning the partiallyreflective output facet, with the notch filter coating applied thereto,at the second end of the laser cavity.
 3. The method of claim 2, furthercomprising: coating the reflective rear facet with the notch filtercoating prior to positioning the reflective rear facet at the first endof the laser cavity.
 4. The method of claim 1 wherein: positioning afirst facet at a first end of the laser cavity includes positioning apartially reflective output facet at the first end of the laser cavity;coating a second facet with a notch filter coating includes coating areflective rear facet with the notch filter coating; and positioning thesecond facet, with the notch filter coating applied thereto, at a secondend of the laser cavity includes positioning the reflective rear facet,with the notch filter coating applied thereto, at the second end of thelaser cavity.
 5. The method of claim 1 wherein forming a laser cavityincludes forming a laser cavity comprising a layer of p-typesemiconductor material, a layer of n-type semiconductor material, and alayer of optically active material disposed between the layer of p-typesemiconductor material and the layer of n-type semiconductor material.6. The method of claim 1 wherein coating a second facet with a notchfilter coating includes coating the second facet with a notch filtercoating that is at least partially reflective of light within a narrowwaveband and substantially transmissive of light outside of the narrowwaveband.
 7. The method of claim 6 wherein coating the second facet witha notch filter coating that is at least partially reflective of lightwithin a narrow waveband and substantially transmissive of light outsideof the narrow waveband incudes coating the second facet with a notchfilter coating that has a first reflectivity for light that is withinthe narrow waveband and a second reflectivity for light that is outsideof the narrow waveband, and wherein the first reflectivity for lightthat is within the narrow waveband is at least twice the secondreflectivity for light that is outside of the narrow waveband.
 8. Themethod of claim 7 wherein coating the second facet with a notch filtercoating that has a first reflectivity for light that is within thenarrow waveband and a second reflectivity for light that is outside ofthe narrow waveband includes coating the second facet with a notchfilter coating that has a first reflectivity greater than 70% for lightthat is within the narrow waveband and a second reflectivity less than30% for light that is outside of the narrow waveband.
 9. The method ofclaim 6 wherein coating the second facet with a notch filter coatingthat is at least partially reflective of light within a narrow wavebandand substantially transmissive of light outside of the narrow wavebandincludes coating the second facet with a notch filter coating that is atleast partially reflective of light within a narrow waveband of lessthan 10 nm and substantially transmissive of light outside of the narrowwaveband of less than 10 nm.
 10. The method of claim 6 wherein coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband includes coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband centered on a nominaloutput wavelength of the laser diode and substantially transmissive oflight outside of the narrow waveband centered on the nominal outputwavelength of the laser diode.
 11. The method of claim 6 wherein coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband and substantiallytransmissive of light outside of the narrow waveband includes coatingthe second facet with a notch filter coating that is at least partiallyreflective of light within a narrow waveband that includes a gain peakof the laser diode and substantially transmissive of light outside ofthe narrow waveband that includes the gain peak of the laser diode. 12.The method of claim 1 wherein coating a second facet with a notch filtercoating includes coating the second facet with a rugate device.